The entire National Party caucus had seen the expenses, after the Whips and Leaders Office received the information last week. Members of Parliamentary Services may have also seen the details.

Speaker Trevor Mallard said on Twitter on Monday night he has asked for a list of people who have seen Mr Bridges' expenses - as well as acknowledging he too has seen it.

"I have already asked for a list of who had it. I do. And an explanation (slow paperwork by VIP) why his (and mine) are bloated by previous quarters figures," Mr Mallard tweeted.

Mr Bridges said he's "very confident" the leak didn't come from his own caucus.

"The Government is looking for every distraction they can rather than focusing on the things they should be," he told reporters on Tuesday morning.

He said he believes every National MP had access to the information.

The Prime Minister Jacinda Ardern said only the Opposition and the Speaker had access to the information.

"[The Speaker] is impartial. He doesn't attend caucus. He presides as an officer of Parliament. It's a really serious allegation to suggest that he could have been involved in some way," Ms Ardern said.

Mr Bridges' caucus members repeatedly said Mr Bridges has been working hard. They were quick to say they have confidence in their leader.

Nikki Kaye said while she can't be certain the leak didn't come from within National, she doesn't believe there is a motive for the leak. She said she saw the document but did not pass it on.

"There are serious questions that have to be asked from a security perspective," Ms Kaye said.

"I can't be confident [it didn't come from National]... National's polling at 45 percent. I'm really proud of the job that Simon Bridges is doing. We are very united."

Nick Smith said he "wasn't aware" of the information but that the expenses are a reflection of Mr Bridges' hard work.

David Bennett said he assumes "National members and others" had access to the information, and said he isn't the leaker.

Simon Bridges' expenses

Mr Bridges spent $84,000 travelling the length of the country in a Crown limousine during his roadshow.

He spent $919 a day - more than people earning the minimum wage take home in a week.